KABUL, Afghanistan — The new U.S. regional envoy landed in Afghanistan on Thursday to help chart President Barack Obama's strategy for peace in this volatile country, a day after a bold Taliban assault demonstrated the insurgency's ability to wreak havoc even in the tightly guarded capital.

A U.S. Embassy spokesman confirmed Richard Holbrooke's arrival late in the day, but declined to give further details about his location or the schedule for his multi-day visit.

Holbrooke's first visit to the country comes amid an increasing sense that the security situation is disintegrating in and around Kabul. On Wednesday, Taliban fighters launched one their most audacious attacks on the capital,
killing 20 people in a coordinated assault
on three government buildings.

Government officials said the mastermind behind the attacks was based in Pakistan, a reminder of the cross-border violence and disputes that have made the battle against the Taliban so difficult. One of Holbrooke's roles as envoy to both countries is to help the Obama administration to design a strategy that will combat Taliban regionally. He is set to meet with President Hamid Karzai, and other high-level officials.

Suicide bombing
"Security measures have been increased 100 percent, particularly at the gates of Kabul," said Abdul Gafar Pacha, the head of the police criminal investigation unit.

In the east, meanwhile, a suicide bomber Thursday blew himself up outside a police station in Sharan, the capital of Paktika province, killing an officer and wounding 10 others, the Interior Ministry said in a statement.

The Taliban regularly target Afghan and foreign troops with suicide and roadside attacks, and other violent incidents have already spiked this year.

In Wednesday's attack, Taliban fighters armed with guns, grenades and suicide vests, they stormed through barricades at the Justice Ministry in the heart of Kabul and a corrections department building to the north. One attacker was killed before he could force his way into a third building, the Education Ministry.

The Taliban claimed responsibility soon after the assault began.

The attack is a reminder of challenges facing Obama as he increases America's focus — and troop levels — in Afghanistan. The new administration has promised up to 30,000 new troops.

All eight attackers died in Wednesday's assaults, leaving the total death toll to 28. Another 57 people were wounded, according to the Interior Ministry.

Amrullah Saleh, the head of Afghanistan's intelligence service, said the attackers sent text messages to a militant leader in Pakistan before the attack.